The performance of radio base station in wireless telecommunication systems may be affected by a number of factors. Specifically, the operational performance of transceivers in radio base stations is of particular importance to service providers because it has a direct effect on the quality of service and experience of the end user. A notable problem that has been well known to plague base station performance is the undesirable generation of intermodulation (IM) products that interfere with the operation of transceivers. Typically complications arising from interference are, in part, induced by connectors, antennas, and other non-linear elements in base stations. The difficulties occur when these intrinsic IM products happen to coincide with the receiver frequencies thus interfering with signal reception. The problem may be exacerbated by the aging of components such as combiners, couplers and duplex filters which operate in association with transceiver elements.
FIG. 1 shows a typical multi-carrier transceiver arrangement together with associated functional components within a radio base station. In this arrangement, the output from a plurality of transmitters i.e. Tx1, Tx2, Tx3, and Tx4 are collected by utilizing a combiner 12. Combiner 12 enables signals from the multiple transmitters to be combined into a single output signal which is then routed to a duplex filter 14. The output signal then emerges from the duplex filter for transmission through antenna 16. It is desirable to use a common antenna for the transmission of output signals and for the reception of incoming signals for efficient operation. The duplex filter 14 permits the use of the common antenna by separating the transmitted signals from the incoming signals. The incoming signals are then routed to a multi-coupler 18 which permits the signals, in accordance with the associated frequency, to be routed to the appropriate receivers Rx1, Rx2, Rx3, or Rx4.
Since the functional components are interconnected, interference generated in any part of the system can affect other elements. For example, IM products accumulated in antenna 16, that fall within the receive frequencies, are routed back to the receivers as shown by path 20. The effects of IM products may be induced by a number of factors, such as the aging of components, bad connections etc. As known by those skilled in the art, IM products which fall within the receiving frequency range may severely interfere with reception of legitimate incoming signals. Additionally, as shown by path 22, interference caused by transmitter operation may be reflected into the receiver path 20 caused by an impedance mismatch with the duplex filter 14 thereby disturbing the receivers. The effect of the disturbance results in a lower signal level thereby degrading receiver performance.
When the bandwith of the IM product is known, it is possible to calculate and preconfigure the receive frequencies such that they will be minimally impacted. For example, a known bandwith of the IM product is approximately equal to the bandwith of the generation signals multiplied by the order of the IM. Thus frequencies can be determined which avoid the interference. Although, this frequency planning approach may work in static situations, it is unsatisfactory for use with systems employing dynamic frequency techniques such as adaptive channel allocation (ACA). Moreover, depending on the particular IM interference, frequency planning places unnecessary restrictions on which frequencies may be used which may not be the most convenient part of the spectrum. ACA techniques, when devoid of effects from IM issues, permit spontaneous frequency hopping to less congested areas of the frequency spectrum for more efficient operation.
As the equipment ages and IM products increasingly become problematic with time. Furthermore, it is difficult to detect precisely when the interference becomes sufficiently high as to degrade base station performance. In view of the foregoing, it is an objective of the present invention to provide a relatively accurate method for detecting when such problematic intermodulation conditions occur.